Bale openers having adjustable grids have been proposed heretofore in the European patent application having the publication number 199 041 and in the U.S. Pat. No. 3,381,341, for example. However, the construction and operation of such grids are subject to some disadvantages.
In conventional bale opener machines, the bales are disposed consecutively in a row parallel to the direction of movement of the bale opener extraction arm carrying the fiber extraction members (e.g. teeth) and the grid through which such members project to pull tufts of fiber from the bales while the arm is travelling along the row. The amount of protrusion of the fiber extraction members through the grid controls in general the rate at which fiber is removed from the bales. However, experience has shown that fiber density variations sometimes occur as between different bales as well as between different layers in a single bale. There are harder and softer bales, and in an individual bale the layer of fibers near the top is apt to be more open and less dense than a layer in the middle of the bale for example. This varying bale layer density affects the amount of fiber removed by the teeth and makes it desirable at times to change the depth of projection of the teeth through the grid.
The depth of projection is defined as the maximum distance which the fiber extraction members or teeth project beneath the grid which slides over the surface of the bales. It differs from the "feed depth," which represents a measure of the extent of vertical adjustment of the entire extraction arm of the bale opener after one transverse of the extraction arm has been completed and before its next movement along the row or group of bales has begun.
The mechanisms proposed heretofore for adjustment of the projection depth by adjusting the grid are relatively expensive. For example, U.S. Pat. No. 3,381,341 uses a plurality of bevel gears for adjustment of the grid, these being relatively expensive per se. To adjust the grid at its two ends, either an additional expensive gear system is required or two separate but suitably synchronized drive motors must be provided for the corresponding bevel gears disposed at the two ends of the grid. Moreover, adjustment of the grid inclination is not possible with such arrangements.
The arrangement shown in EP 199 041 allows adjustment both of the projection depth and of the grid inclination, but ultimately requires four drive motors which must be synchronized at least in pairs.